Chapter XII
WORK OF THE AUXILIARIES[ToC]
CHAPTER XII
WORK OF THE AUXILIARIES
Mine-sweeping methods—Indicator nets—Heavy losses—Brilliant rescues.
Without going into technical details, I will now give a brief explanation of the usual methods employed by the mine-sweeping trawlers of the Harwich base. Two trawlers steaming abreast at about four hundred yards distance apart tow a sweep wire eight hundred yards in length, an end of which is attached to each trawler. The wire thus drags astern in a great loop, which is kept at the requisite depth—that is, at a depth well exceeding the draught of the deepest ship which would travel across that area—by kites. This sweep wire is serrated, so that when towing it quickly saws through the moorings of the mines, which are thus released and rise to the surface. When two or more pairs of trawlers are sweeping in unison they adopt what may be termed an échelon formation. The second pair of mine-sweepers follows the first pair, at a safe distance astern, on a parallel course, but on an alignment that causes the space swept by the following pair of vessels to somewhat overlap that swept by the leading pair, so that no unswept space is left between the two. If a third pair of vessels follows, it takes up a similar position astern of the second pair; and so on, if there be other pairs engaged in the sweep. When a strong cross tide is running, to carry out this operation accurately is no easy task. But the skilled North Sea fishermen who man the trawlers are the right men for this sort of work. They rapidly acquire all the tricks of sweeping, and soon learn to detect a mine that has been caught in the sweep by the singing of the sweep wire, the feel of it, and other delicate signs. The mine-sweeping trawlers are accompanied by a vessel whose duty it is to sink or explode by rifle fire the released mines as they appear on the surface.
The above explanation of mine-sweeping, of course, deals with very elementary matter. For during the war this science has made immense progress, and volumes could be written on it. Many are the ingenious contrivances that have been introduced to improve the efficiency of the sweep. In fact, in all our operations, offensive and defensive, below the surface of the sea weird new inventions play an important part. Take, for example, that grimly humorous invention the indicator net, to lay which was one of the duties of the drifters of the Harwich Force. In its early form this was a fine wire net, which, when run into by a submarine travelling below the surface, was dragged from its moorings and remained attached to the enemy, accompanying him whithersoever he went, not impeding his progress, and possibly unnoticed by him, but dooming him to destruction. For attached to this net by a long line was a buoy containing a torch which was lighted automatically when the strain of the tow came on the buoy. So the unconscious enemy travelled on underneath, announcing his presence by the flaming torch which accompanied him overhead, thus enabling the watchful British patrol boats to close in on him and effect his destruction with depth charges. The above is an ideal case, for in practice the operation was by no means always so simple or so successful. But that early type of indicator net has been superseded by a much more deadly invention.